The hybridization technique referred to by the present invention is confined to hybridization by fusion. This technique, which is widely known, uses bumps made of a fusible material such as a tin-lead alloy, tin-indium alloy or even pure indium.
Briefly, this hybridization technique by fusion involves:                depositing bumps of fusible material on bonding pads produced on one of the components, said pads consisting of a material that can be wetted by the material that constitutes the solder bumps;        and then providing the other component that is to be hybridized with pads also consisting of a material that can be wetted by the material that constitutes the solder bumps, said pads being arranged substantially opposite the pads of said first component when said second component is mounted on the first component;        then, by increasing the temperature until a temperature in excess of the melting temperature of the material that constitutes the bumps is reached, obtaining fusion of the latter until the desired result is achieved, namely hybridization of the second component on the first component, said bumps creating a mechanical and/or electrical link between the pads of each of the components.        
For components having relatively small dimensions, the accuracy with which said components are positioned relative to each other when the upper component is mounted on the lower component is not very critical. In fact, the surface tension phenomena that affect hybridization bumps during the fusion process produce automatic alignment of said components. In addition, these surface tension phenomena make it possible to compensate, at least partially, for the thermal expansion phenomena that affects two components having different thermal expansion coefficients and which result in the movement of the pads of one component relative to those of the other component.
For components having larger dimensions, one known technical solution associated with the problem of differential expansion of components involves compensating for expansion phenomena by taking action in terms of the actual design of the components.
Thus, Document FR 2,748,849 proposes moving the wettable surfaces of the component that is to be hybridized linearly and homothety so that, at the hybridization temperature, said wettable surfaces are located substantially opposite each other and not out of alignment with the wettable surfaces or pads of the other component, thereby compensating for this differential expansion.
FIGS. 1a and 1b schematically show the underlying principle of the technical solution adopted in this document, FIG. 1a showing a schematic cross-sectional view before hybridization of a component system that is to be hybridized at ambient temperature and FIG. 1b showing a view similar to FIG. 1a but at the hybridization temperature of the components.
In FIGS. 1a and 1b, 1 denotes the substrate, made of silicon for example, and 2 denotes the cover intended to be mounted on the substrate. Substrate 1 has wettable areas 3, typically made of gold, with a prior barrier based on an alloy of titanium or nickel on which hybridization bumps 4 are deposited. Wettable surfaces 5 are produced on the lower surface of cover 2 in the same way, but without any hybridization bumps. According to the teaching of this document, at ambient temperature the wettable surfaces 5 of cover 2 are not located opposite the wettable surfaces 3 of substrate 1 when said cover is mounted on said substrate.
However, because of the difference in the thermal expansion coefficients of the substrate α1 and of the cover α2 respectively, when the hybridization temperature which exceeds the melting temperature of the material that constitutes bumps 4 is reached, wettable surfaces 5 of said cover move and position themselves substantially opposite the wettable surfaces 3 of substrate 1 so that hybridization is possible as shown in FIG. 1b. 
However, although the process described in this document works satisfactorily for arrays of relatively small size, especially arrays measuring less than 1000×1000 pixels, arrays having larger dimensions encounter a certain number of technical problems.
Firstly, the design of the components according to this document is based on the principle of offsetting the wettable surfaces because of thermal expansions that are substantially uniform relative to a barycenter. Unfortunately, because of constraints associated with the actual fabrication of these components, obtaining perfect, regular surfaces, especially those surfaces of the components in question that are intended to be opposite each other, is an ideal that is difficult to achieve and what the technology describes as fixed points or sticking points shown by arrow A in FIG. 2a are often created. Given this, because of these sticking points, thermal expansion, especially that of the cover in the example described, will take place from the sticking point rather than from a substantially central point of the array and will cause considerable misalignment of the wettable surfaces that are farthest away from the sticking point as shown by arrow B in FIG. 2a. 
In fact, if L denotes the distance between the two most extreme wettable areas of the substrate and if this distance comprises N pixels, this gives the equation L=(N−1)×pitch, the pitch being commonly defined as the distance separating two consecutive pixels.
Consequently, if D denotes the misalignment between one bump or a wettable area of substrate 1 and the wettable area with which it is intended to cooperate on cover 2, this gives the following equation:D=(α2−α1)×(Th−Ta)×L/2=(α2−α1)×(Th−Ta)×(N−1)/2×pitchin accordance with the teaching of the above-mentioned document where Th is the hybridization temperature and Ta is ambient temperature.
Thus, by way of example, for an array of cadmium telluride CdTe comprising 4000×4000 pixels hybridized on silicon with a pitch of 10 μm and measuring 40×40 cm, having a variation in thermal expansion coefficients α2-α1 of the order of 3×10−6, the differential expansion D for a temperature difference of 170° C. equals 1.2 pitch increments.
In other words, when the chips are deposited, the penultimate bump N−1 on the periphery of the lower chip, in this case substrate 1, is located opposite wettable surface N of the upper chip 2. This compensation for expansion results in misalignment equal to one pixel, as shown in FIG. 2b (on the right-hand side). Besides linear expansion, practical experience has demonstrated the occurrence of rational or circular expansion and even other types of movement.
In other words, the technical problem which the present invention intends to solve is the fact that the barycenter of expansion is not controlled due to the existence of sticking points created by the topologies adopted by the various technologies. The most prominent point of the surfaces that are in contact may constitute the center of expansion and thus disrupt hybridization of components. Although, for small-size components, this problem is mitigated by the fact that misalignment remains less than the value of the spacing pitch, with larger components this defect may have a significant impact on manufacturing yields.